Copolyester-carbonates are known thermoplastic materials which, due to their many advantageous properties, find use as thermoplastic engineering materials. The copolyester-carbonates exhibit, for example, excellent properties of toughness, flexibility, impact resistance and high heat distortion temperatures. However, the copolyester-carbonates, due to their relatively high melt viscosities, are generally relatively difficult to process. Furthermore, there are certain applications where copolyester-carbonate resins exhibiting a greater degree of hydrolytic stability than that normally possessed by copolyester-carbonate resins are needed.
These problems of providing improved processability and greater hydrolytic stability have been met by the prior art by incorporating into the copolyester-carbonate compositions various additives. These additives have consisted of compounds which improve the processability of the copolyester-carbonate compositions and compounds which improve the hydrolytic stability of these compositions. The addition of these additives while generally being effective in improving the processability of the compositions and the hydrolytic stability of the copolyester-carbonate compositions sometimes adversely affects some of the other advantageous properties thereof, such as the heat distortion temperature and the optical properties such as transparency. It would thus be very advantageous if copolyester-carbonates could be provided which retained substantially most of their other advantageous properties and simultaneously exhibited improved processability, or improved hydrolytic stability.
It is, therefore, an object of the instant invention to provide copolyester-carbonate compositions exhibiting improved processability while simultaneously retaining, to a substantial degree, most of the other advantageous properties of copolyester-carbonates, particularly their heat distortion temperatures and optical transparency; and provide copolyester-carbonate compositions exhibiting improved hydrolytic stability.